Association between the Mediterranean Diet Index and self-reported Gingival Health Status Indicators in a population of Chilean adults: a cross-sectional study

Abstract Despite the recognized impact of diet on non-communicable diseases, the association between the Mediterranean diet and periodontal diseases is still uncertain. This study aimed to determine the association between adherence to the Mediterranean Diet Index (MDI) and self-reported gingival health status in Chilean adults, exploring the feasibility of using validated web-based survey questionnaires. Methodology Cross-sectional data were collected from a representative sample of a population of Chilean adults (18-60 years old) using a low-cost and time-saving methodology. By the PsyToolkit platform, anonymous survey data were downloaded and analyzed in bivariate (crude) and backward stepwise selection multivariate logistic regression models adjusted for sociodemographic determinants, smoking, and dental attendance using STATA 17. Odds ratios (OR) [95% confidence intervals] were estimated. Results In total, 351 complete statistical data were mostly obtained from female university students who had never smoked and reported having visited a dentist in the previous year. Multivariate regression models showed an association between MDI and very good/good gingival health status (OR 1.18 [95% CI 1.04-1.34], p=0.013), absence of bleeding on toothbrushing (OR 1.12 [95% CI 1.01-1.25], p=0.035), and absence of clinical signs of gingival inflammation (OR 1.24 [95% CI 1.10-1.40], p<0.001), after controlling for age, sex, educational level, smoking, and dental attendance. Conclusions We associated adherence to the Mediterranean diet with better self-reported gingival health status in a population of Chilean adults in an entirely web-based research environment. Longitudinal studies with random sampling are required to establish the effect of diet on gingival and periodontal health. Nevertheless, this evidence could contribute to the design of low-cost surveillance programs to reduce the burden of periodontal disease and related “common risk factors”.


Introduction
Non-communicable diseases (NCDs) are highly prevalent chronic diseases that strongly contribute to the global burden of disease and are one of the leading causes of mortality worldwide. 1 Periodontal diseases (PDs) are NCDs due to sharing pathogenic mechanisms that link them from a preventive and therapeutic perspective, and sociodemographic determinants including age, sex, and educational level, as well as risk factors such as smoking, sedentary lifestyle, and obesity. 2 Plaque-induced gingivitis is an inflammatory response of gingival tissues resulting from bacterial plaque accumulation located at and below the gingival margin. If supra-and subgingival plaque is not removed, an inflammatory immune response is triggered in a susceptible host, which can lead to progressive destruction of tooth-supporting tissues, causing periodontitis and subsequent tooth loss. 3 Recently, studies have investigated the potential effects of nutritional supplements on the development and progression of PDs. 4 Although the preventive role of diet in the course of NCDs has been widely documented, 1 knowledge regarding its role in PDs is lacking.
Diets rich in vegetables have high anti-inflammatory characteristics due to their high content of vitamins, flavonoids, polyphenols, nitrates of vegetable origin, omega-3, and essential minerals such as calcium, magnesium, and zinc, preventing cardiovascular diseases, the incidence of cancer, neurodegenerative diseases, and type 2 diabetes mellitus, significantly reducing C-reactive protein, a marker associated with complications and mortality from NCDs. 5 These nutrients have shown significant improvements in the clinical and microbiological parameters of periodontal disease, thus suggesting a promising preventive and therapeutic value. 4 However, dietary patterns are a broader picture of food and nutrient consumption and may be more predictive of disease risk than individual food or nutrients. 6 The Mediterranean diet is primarily a plant-based dietary pattern that includes the daily intake of whole grains, olive oil, fruits and vegetables, legumes, nuts, and a small quantity of animal protein, with fish and seafood as the preferred animal protein. 7 Although the available evidence shows a potentially beneficial effect of the Mediterranean diet on gingival health status, it is still unable to allow a high certainty. 4 The risk of bias is high due to measurement bias given the use of non-standardized dietary indices. 4 Furthermore, the effects of sociodemographic covariates that could influence adherence to the Mediterranean diet and healthy oral behavior have not been considered. 4 Therefore, further studies in a real context are required to clarify the association between the Mediterranean diet and gingival health indicators.
One way of inexpensive epidemiological study for PDs and nutrition surveillance is self-reporting measures and indices, especially useful when clinical examination is unfeasible, that is, in a low-resource setting or when clinical measurements are unfeasible, such as during the COVID-19 quarantine. These measures have demonstrated acceptable sensitivity and reliability in the evaluation of PDs and dietary patterns. [8][9][10] Questions about gum health/disease, gum treatment, loose teeth, bone loss, tooth appearance, floss, and mouthwash use showed moderate to high accuracy in identifying gingivitis and periodontitis, with an area under the receiver operating characteristic curve (ROC) of 0.837. 10

Setting and Participants
Data were obtained by a voluntary self-reported anonymous survey available on the PsyToolkit platform 17,18 for adults aged between 18 and 60 years from the community of the University of Chile. The inclusion criteria were being at least 18 years old and having the time and willingness to answer the survey.
Exclusion criteria were based on well-known biological confounding factors for gingival inflammation such as pregnancy and use of anti-inflammatories or systemic antibiotics. 19 Other potential confounders were included, analyzed, and/or properly adjusted in the final model to achieve greater external validity.   This self-reported instrument assesses the frequency and quantity consumed of 14 food groups according to the recommendation derived from a Mediterranean diet, namely vegetables (3 or more servings per day), legumes (more than 2 times per week), nuts (more than 2 handfuls per week), fruits (2 or more servings per day), whole grains (2 or more servings per day), fermented and skimmed dairy (more than 1 serving per day), whole dairy (no consumption), fish and seafood (more than 2 times a week), white and lean red meats (5 to 8 times a week), fatty red meats and processed meats (less than 1 time a week), olive oil (more than 3 teaspoons a day), canola oil (regular consumption) and avocado (more than 3 units per week), wine (1 to 2 glasses per day, 4 or more days per week), sugar (less than 4 teaspoons per day) and snacks and/or sweetened beverages (no consumption). The detailed algorithm for calculating the MDI score used in this study is presented in the original article.

Smoking
The question from Form 1 of the National Health Survey (NHS) 2016-17 was applied "Do you currently smoke cigarettes?" whose responses were 1. Yes, one or more cigarettes per day, 2. Yes, occasionally (less than one cigarette per day), 3.
No, I stopped smoking; 4. No, I have never smoked. Physical activity The question of Form 1 of the National Health Survey (NHS) 2016-17 was applied "In the last month did you practice sport or engage in physical activity outside your working hours, for 30 minutes or more each time?" whose answers were 1. Yes, three or more times per week, 2. Yes, once or twice per week, and 3. Yes, less than four times a month, 4. I did not practice sports during the month.
NHS 2016-2017 27 1= Yes, three or more times per week 2= Yes, once or twice per week 3= Yes, less than four times a month 4= I did not practice sports during the month

Hygiene and oral health habits
How many times a day do you brush your teeth?
This question was validated 26 , whose answers were 1. Less than once per day, 2. Once a day, 3. Twice a day and 4. Three or more A reliable self-report questionnaire was obtained, with a total Cronbach's alpha of 0.73 and a Kappa-index ranging from 0.41 to 0.77 between the different questions. 26 1= Less than once per day 2= Once a day 3= Twice a day 4= Three or more How would you rate your toothbrushing?

Dental attendance
The NHS 2016-17 Form 1 question "When was the last time you visited the dentist?" whose responses were 1. Less than six months ago, 2. Between 6 months and a year ago, 3. More than one year and less than two years ago, 4. Two or more, but less than five years ago, 5. Five or more years ago and 6. Never visited.

Self-reported gingival health status indicators (SGH) 26
How would you rate your gum health?
A reliable self-report questionnaire was obtained, with a total Cronbach's alpha of 0.73 and a Kappa-index ranging from 0.41 to 0.77 between the different questions. 26 0= Average/Bad (3 and 4) 1= Very good/Good (1 and 2) During toothbrushing, do your gums bleed?
0= Yes (1,2 and 3) 1= No (4) In the last month, have you noticed that your gums are reddish and/or swollen?
The alternatives were 1. Always, 2. Often, 3. Sometimes and 4. Never. presence or absence of systemic diseases, that is, long-term (chronic) diseases that affect several organs and tissues, were also self-reported.

Dietary assessment
The Chilean MDI is an 14-item instrument 16 based on a previous Mediterranean eating score that was adapted to Chilean dietary habits and assesses the frequency and quantity consumed of 14 food groups according to the recommendation derived from a Mediterranean diet, namely vegetables (3 or more servings per day), legumes (more than 2 times per week), nuts (more than 2 handfuls per week), fruits (2 or more servings per day), whole grains (2 or more servings per day), low fat and fermented dairy (more than 1 serving per day), whole fat dairy (no consumption), fish and seafood (more than 2 times a week), white and lean red meats (5-8 times a week), fatty red meats and processed meats (less than 1 time a week), olive oil (more than 3 teaspoons a day), canola oil (regular consumption) and avocado The output of the regression models was presented as odds ratios (OR) with 95% confidence interval (95% CI). Statistical significance was p<0.05. Kruskal-Wallis test for educational level, significant differences were found in the MDI scores between high school (8 (IQR 2)) and university (9 (IQR 2)) (p<0.05).

Results
Regarding smoking, no statistically significant difference was shown in the MDI score between the group that currently smoked (8.05±1.89) and the group that did not (8.55±1.98), according to Student's t-test (p>0.05). Moreover, when the mean MDI of the group that visited the dentist in the previous year Association between the Mediterranean Diet Index and self-reported Gingival Health Status Indicators in a population of Chilean adults: a cross-sectional study 2023;31:e20230100 7/13 (8.46±2.07) was compared with the group that did not (8.42±1.83), there was no significant difference according to Student's t-test (p>0.05).

Self-reported gingival health status
Regarding sociodemographic variables and SGH, no statistically significant differences were found between age, sex, and binary categories of SGH (p>0.05).
When the SGH categories were compared based on current smoking habit, significant differences were found between groups for all SGH (p<0.05) after applying Fisher's exact test. However, when these differences were explored in the binary categories of each SGH using the Mann-Whitney U test, no significant differences were found between groups (p>0.05).
Moreover, there were no significant differences between the groups for dental attendance regarding all SGH (p>0.05).

Mediterranean diet and self-reported gingival health status: relationship between outcome measures
On the other hand, statistically significant differences were found according to dietary quality and the questions "During toothbrushing, do your gums bleed?" (p=0.002) and "In the last month, have you noticed that your gums are reddish and/ or swollen?" (p=0.004) using Fisher's exact test.
Furthermore, statistically significant differences were

Multivariate regression analysis
To control possible confounders, the full multivariate model was adjusted for theoretical covariates (dashed line) and observed in bivariate linear correlation models (solid line), as shown in the DAG (Figure 3). Note: 1) "How would you rate your gum health?" (dichotomous), 2) "During toothbrushing, do your gums bleed?" (dichotomous), 3) "In the last month, have you noticed that your gums are reddish and/or swollen?" (dichotomous), 4) MDI (continuous), 5) age, 6) sex, 7) educational level, 8) dental attendance (dichotomous), and 9) smoking (dichotomous). educational level, and dental attendance (p<0.05), with an OR for the adjusted model of 1.18 (95% CI 1.04-1.34). However, the association between the MDI score and self-reported absence of bleeding due to brushing was significant with an OR of 1.12 (95% CI 1.01-1.25), adjusted for dental attendance. For the association between the MDI score and self-perception of signs of gingival inflammation, a significant association was found, which was not attenuated after adjusting for age, sex, educational level, and dental attendance in the last year, with an OR of 1.24 (95% CI 1.10-1.40) (p<0.001).

Model fit
The p-values for the Hosmer-Lemeshow test in the adjusted models were greater than 0.1, indicating little evidence of poor goodness-of-fit. Regarding the post-estimation tests for the adjusted models, the test is based on the idea that if a regression-type equation is well specified (_hat<0.05), no additional independent variable should be significantly above the chance level (_hatsq>0.05), which was met for all the adjusted models (Table 3).   to the pathophysiology of periodontal diseases. [36][37][38] These mechanisms are preceded by epigenetic modifications due to the Mediterranean diet, improving insulin metabolism and, consequently, preventing insulin resistance in non-diabetic patients 39 and thus controlling the indirect etiopathogenesis of PDs.

Strengths and Limitations
This is the first study in Chile to answer this research question using correctly specified and adjusted multivariate models based on statistical data from a representative sample of Chilean adults, particularly from a university community, collected using a low-cost and time-saving methodology. Thus, this study is a good approximation and precursor for future lines of research in Chile on the common dietary risk factors of NCDs, particularly PDs. However, these findings should be cautiously interpreted.
Online self-report surveys are low-cost and, in this study, a feasible methodology for conducting studies in complex circumstances. Consequently, they could be applied in a multicenter setting for active surveillance of PDs in the most affected populations in the southern cone, with a high burden of the disease; however, sometimes without resources to characterize, prevent, or treat it. In this sense, PsyToolkit 17,18 allows an intuitive, complete, and dynamic coding and user interfaces, enabling the self-application and subsequent automatic estimation of complex algorithms such as the MDI, an indicator that can be a sufficient and useful diet screener in dental studies. 15 Moreover, PsyToolkit has no response limits. 17,18 Thus, probabilistic sampling can be performed for large populations without any major drawbacks. Therefore, one way to reach a larger and heterogeneous population and, consequently, improve the representativeness would be to incorporate this or another diet quality index, together with SGH, in future national health surveys or large-scale governmental surveys.
Regarding data analysis and interpretation, the models were adjusted for the main South American risk indicators reported, which are also the most used covariates in NCD-related nutritional epidemiology. 21 The covariates used in our study were adequate for the proposed objective and expected internal validity.
However, longitudinal studies are necessary to test the causal relationships proposed in the DAG, specifically using data that allows adjustment for other habits, such as oral hygiene habits or physical activity, to identify the impact of diet on periodontal health status as a risk factor.
It is essential to highlight some of the characteristics observed and explained by the convenience sampling strategy and recognize the fact that the collected data were from population most likely to complete online surveys. 40 A large part of the population self-reported healthy lifestyles and habits, including regular physical activity, a high-quality diet, non-smoking habits, or effective toothbrushing performance. Furthermore, this population has regular access to dental care.
These factors are associated with the educational level of our population, 41 which involves an economic determinant of access to universities that biases the selection of participants.
On the other hand, we assumed that the university population has a high self-perception of PDs, possibly related to a greater concern and possibility of sustaining a healthy lifestyle, which corroborates the findings of the SGH. Thus, an essential aspect to Furthermore, we used the dichotomous variable "visit to the dentist in the last year" as a surrogate variable for increased plaque removal, 22 assuming that this would be reinforced by oral hygiene instruction or performed professionally at the same visit. However, we had no data on the nature of visits, whether for periodontal therapy, by public or private services, or if the person's ability to stabilize their disease was evaluated, or whether dietary counseling for PDs prevention was provided during these visits. However, we assumed that almost half of the professionals would perform some type of nutritional care, for example, with dietary analysis and subsequent nutritional or dietary counseling. 23 Studies are needed that also specify this information at the national level as well as the circumstances and reasons for performing such counseling.